Attributesare data elements that describe Nodes. Clientscan access Attributevalues using Read, Write, Query, and Subscription/MonitoredItem Services. These Servicesare defined in OPC 10000-4.

Attributesare elementary components of NodeClasses. Attributedefinitions are included as part of the NodeClassdefinitions in Clause 5and, therefore, are not included in the AddressSpace.

Each Attributedefinition consists of an attribute id (for attribute ids of Attributes, see OPC 10000-6), a name, a description, a data type and a mandatory/optional indicator. The set of Attributesdefined for each NodeClassshall not be extended by Clientsor Servers.

When a Nodeis instantiated in the AddressSpace, the values of the NodeClass Attributesare provided. The mandatory/optional indicator for the Attributeindicates whether the Attributehas to be instantiated.